First, it must be edited. Several rounds of editing are often needed to address problems with the content (such as a gap in an argument or an inconsistency in a fictional universe) and formal flaws in the writing (such as spelling and punctuation errors). I can do that editing. If you wish, I can edit more proactively as well, suggesting improvements even where there are no mistakes.
If you want a print edition, it has to be laid out. An amateurish design can make people take a book less seriously, so it’s a good idea to have your book laid out by a professional. For a sample of my design work, take a look at this project on Amazon. Depending on what kind of cover you want, I can create it or find the right person to do so. I can also help you pick the right printing company (or companies: sometimes you’re better off with two), and I can work with the printers.
Once a book has been laid out, it should be proofread.
If you want an ebook edition, the text needs to be formatted for that. If any changes were made during layout and proofreading for the print edition, those changes need to be carried over to the ebook. So if I’ve been involved at one of those stages, it’s a good idea to stick with me through preparation of the ebook file. I can also create an ebook cover based on the print cover. And if there is no print cover, I can either create an ebook cover or find the right person to do so, depending on what kind of cover you want.